A solution is a homogenous mixture of 2 or more substances. The solute is(are) the substance(s) present in the smaller amount(s). The solvent is the substance present in the larger amount.

An electrolyte is a substance that, when dissolved in water, results in a solution that can conduct electricity. A nonelectrolyte is a substance that, when dissolved, results in a solution that does not conduct electricity. nonelectrolyte weak electrolyte strong electrolyte

A saturated solution contains the maximum amount of a solute that will dissolve in a given solvent at a specific temperature. An unsaturated solution contains less solute than the solvent has the capacity to dissolve at a specific temperature. A supersaturated solution contains more solute than is present in a saturated solution at a specific temperature. Sodium acetate crystals rapidly form when a seed crystal is added to a supersaturated solution of sodium acetate.

Concentration Units The concentration of a solution is the amount of solute present in a given quantity of solvent or solution. Molarity (M) M = moles of solute liters of solution

Three types of interactions in the solution process: solute-solute interaction (separating the solute) solvent-solvent interaction (overcoming intermolecular forces) solvent-solute interaction

Steps 1 and 2 require energy, since forces must be overcome to expand the solute and solvent. Step 3 usually releases energy. Steps 1 and 2 are endothermic and step 3 is often exothermic. Enthalpy change: enthalpy (heat) of solution (∆H soln ) is the sum of the ∆H values for the steps: ∆H soln = ∆H 1 + ∆H 2 + ∆H 3

(a) ΔH soln has a negative sign (exothermic) if step 3 releases more energy than that required by 1 and 2 (b) ΔH soln has a positive sign (endothermic) if steps 1 and 2 require more energy than is released in 3

“like dissolves like” Two substances with similar intermolecular forces are likely to be soluble in each other. non-polar molecules are soluble in non-polar solvents CCl 4 in C 6 H 6 polar molecules are soluble in polar solvents C 2 H 5 OH in H 2 O ionic compounds are more soluble in polar solvents NaCl in H 2 O or NH 3 (l) What factors affect solubility?

Temperature and Solubility Solid solubility and temperature – the solubility of most solids increases with temperature. solubility increases with increasing temperature solubility decreases with increasing temperature due to entropy (not covered yet)

Temperature and Solubility Gas solubility and temperature solubility usually decreases with increasing temperature (more energy to escape from solvent)

A suspension of tiny particles in some medium is called a colloidal dispersion, or a colloid. Dispersion Medium Dispersed Phase Type of colloid Example Gas Liquid Aerosol Fog, mist Gas Solid Aerosol Smoke Liquid Gas Foam Whipped cream Liquid Emulsion Mayonnaise, hair cream Liquid Solid Sol Paints, cell fluids Solid Gas Foam Pumice, plastic foams Solid Liquid Gel Jelly, cheese Solid Solid Sol Ruby glass (glass with dispersed metal) The Tyndall effect is used to distinguish between a suspension and a true solution. Light is scattered by the suspended particles in a colloid.